Hi. These are my first steps at writing SOAP messages for Zimbra, and of course I have errors, but I really don't know how those error report can help me to figure out what's wrong ?

Code:
2012-10-11 16:10:28,437 WARN  [btpool0-26] [mid=1;] SoapEngine - handler exception

java.lang.NullPointerException

	at com.zimbra.cs.service.mail.CalendarRequest.handleMsgElement(CalendarRequest.java:135)
	at com.zimbra.cs.service.mail.CreateCalendarItem.handle(CreateCalendarItem.java:69)
	at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEngine.java:412)
	at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.java:287)
	at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.java:158)
	at com.zimbra.soap.SoapServlet.doWork(SoapServlet.java:303)
	at com.zimbra.soap.SoapServlet.doPost(SoapServlet.java:217)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
	at com.zimbra.cs.servlet.ZimbraServlet.service(ZimbraServlet.java:206)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:814)
	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:390)
	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:218)
	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:422)
	at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
	at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at org.mortbay.jetty.handler.rewrite.RewriteHandler.handle(RewriteHandler.java:230)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at org.mortbay.jetty.Server.handle(Server.java:326)
	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:585)
	at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:988)
	at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
	at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:415)
	at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:429)
	at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:451)

2012-10-11 16:11:07,046 WARN  [btpool0-26] [mid=1;] SoapEngine - handler exception
My question IS NOT about what when wrong in my particular case, but general tips on how one could debug debug his app when doing SOAP with zimbra.

Thanks for any tips shared.